Symbionts are adapted to work with corals: Many corals have formed mutualistic associations with dinoflagellate symbionts, which are thought to provide nutrients and other benefits. To examine the underlying genetics of this association, S. Lin et al. sequenced the genome of the endosymbiont dinoflagellate Symbiodinium kawagutii. The genome includes gene number expansions and encodes microRNAs that show complementarity to genes within the coral genome. Such microRNAs may be involved in regulating coral genes. Furthermore, coral and S. kawagutii appear to share homologs of genes encoding specific nutrient transporters. The findings shed light on how symbiosis is established and maintained between dinoflagellates and corals. Science , this issue p. 691

The chloroplasts of most dinoflagellates are unusual in that they are surrounded by three membranes and contain the carotenoid peridinin. The ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) in dinoflagellate chloroplasts was found here to also be unusual. Unlike other eukaryotes, dinoflagellates containing peridinin use a form of RuBisCO (form II) previously found only in some species of proteobacteria. Furthermore, this RuBisCO is not encoded in the chloroplast DNA, as is the case in other organisms, but is encoded by the nuclear DNA. The unusual nature of this enzyme and location of its gene support the idea that dinoflagellate chloroplasts may have had a distinctive evolutionary origin.

A 10-fold circadian variation in the amount of luciferin binding protein (LBP) in the marine dinoflagellate Gonyaulax polyedra is reported. This protein binds and stabilizes luciferin, the bioluminescence substrate. In early night phase, when bioluminescence is increasing and LBP levels are rising in the cell, pulse labeling experiments show that LBP is being rapidly synthesized in vivo. At other times, the rate of LBP synthesis is at least 50 times lower, while the rate of synthesis of most other proteins remains the same. The LBP mRNA levels, as determined by in vitro translations and by RNA (Northern) hybridizations, do not vary over the daily cycle, indicating that circadian control of bioluminescence in this species is mediated by translation.